Display screen or portion thereof with a graphical user interface



FIG. 1 is a front view of a display screen or portion thereof with a transitional graphical user interface showing a first image in a sequence according to our new design;

FIG. 2 is a front view thereof showing a second image in the sequence; and,

FIG. 3 is a front view thereof showing a third image in the sequence.

The outermost broken line illustrates a display screen or portion thereof and forms no part of the claimed design. The appearance of the transitional image sequentially transitions between the images shown in FIGS. 1-3. The process or period in which one image transitions to another image forms no part of the claimed design. The remaining broken lines represent elements of the display screen or portion thereof with a graphical user interface that form no part of the claimed design. 

CLAIM We claim the ornamental design for a display screen or portion thereof with a graphical user interface, as shown and described. 